The Core Virology Laboratory will perform protocol mandated virology studies on all patients entered into ACTG clinical trials at the Hospital of the University of Pennsylvania, Thomas Jefferson University Hospital (subunit), and Girard Medical Center addiction clinic (site). We consider as routine studies the following: HIV cultures, serum p24 antigen assays, EIA and Western blots to detect antibody to HIV, and PCR for HIV DNA detection in cells. Although we are proposing to become a new ACTG Core Laboratory, we have extensive experience in these and other diagnostic virology tests. In addition to routine tests described above, the Core Laboratory will perform more specialized tests on certain patients entered into ACTG protocols. These include: i) Quantitative studies, using virus culture and PCR, to follow the response of patients to antiretroviral therapy. Quantitative cultures will measure virus titers in plasma and cerebral spinal fluid, while quantitative PCR will determine HIV DNA copy number in peripheral blood mononuclear cells. ii) Intravenous drug users who are enrolled in studies will be screened for HTLV-1, and -2 infection. HTLV infection is common in the IVDU population, and may be a confounding variable in the course of HIV-1 disease and response to therapy. iii) HSV, VZV, and CMV isolates will be monitored for emergence of resistance to new or currently available antivirals by examining the susceptibility of patient isolates to these antiviral agents. Many tests performed in the Core Laboratory, particularly screening for HTLV infection, will be offered to investigators at other ACTG sites to broaden the scope of virology tests available to monitor patients.